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<h2 id="基本流程"><a href="#基本流程" class="headerlink" title="基本流程"></a>基本流程</h2><ol>
<li>导入驱动jar包<ol>
<li>在项目中新建libs目录(和src同级)</li>
<li>将mysql-connector-java-8.0.20.jar复制到libs目录中</li>
<li>右键libs目录，将该目录添加到library(add as library)</li>
</ol>
</li>
<li>注册驱动</li>
<li>获取数据库连接对象Connection</li>
<li>定义sql</li>
<li>获取执行sql语句的对象statement</li>
<li>执行sql，接收返回结果</li>
<li>处理结果</li>
<li>释放资源</li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">JDBCDemo1</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        <span class="comment">//注册驱动</span></span><br><span class="line">        Class.forName(<span class="string">&quot;com.mysql.cj.jdbc.Driver&quot;</span>);</span><br><span class="line">        <span class="comment">//获取数据库连接对象</span></span><br><span class="line">        Connection connection= DriverManager.getConnection(<span class="string">&quot;jdbc:mysql://cdb-cd3ybvc6.cd.tencentcdb.com:10056/weixinNews&quot;</span>,<span class="string">&quot;root&quot;</span>,<span class="string">&quot;renboyu&quot;</span>);</span><br><span class="line">        <span class="comment">//定义sql语句</span></span><br><span class="line">        String sql=<span class="string">&quot;SELECT * FROM WEIBO WHERE TITLE LIKE &#x27;%韩国%&#x27;;&quot;</span>;</span><br><span class="line">        <span class="comment">//获取执行sql的对象Statement</span></span><br><span class="line">        Statement statement=connection.createStatement();</span><br><span class="line">        <span class="comment">//执行sql语句</span></span><br><span class="line">        ResultSet set=statement.executeQuery(sql);</span><br><span class="line">        <span class="comment">//打印结果</span></span><br><span class="line">        <span class="keyword">while</span> (set.next())&#123;</span><br><span class="line">            String title=set.getString(<span class="string">&quot;TITLE&quot;</span>);</span><br><span class="line">            System.out.println(title);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">//释放资源</span></span><br><span class="line">        statement.close();</span><br><span class="line">        connection.close();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="更规范的流程"><a href="#更规范的流程" class="headerlink" title="更规范的流程"></a>更规范的流程</h4><p>（尽量避免直接抛出错误）</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">JDBCDemo2</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line">        Connection connection=<span class="keyword">null</span>;</span><br><span class="line">        Statement statement=<span class="keyword">null</span>;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="comment">//注册驱动</span></span><br><span class="line">            Class.forName(<span class="string">&quot;com.mysql.cj.jdbc.Driver&quot;</span>);</span><br><span class="line">            <span class="comment">//定义sql语句</span></span><br><span class="line">            String sql=<span class="string">&quot;insert into stuMess VALUES(null,&#x27;Leslie&#x27;,&#x27;CS&#x27;,&#x27;95&#x27;);&quot;</span>;</span><br><span class="line">            <span class="comment">//获取数据库连接对象</span></span><br><span class="line">            connection= DriverManager.getConnection(<span class="string">&quot;jdbc:mysql://cdb-cd3ybvc6.cd.tencentcdb.com:10056/jdbcTest&quot;</span>,<span class="string">&quot;root&quot;</span>,<span class="string">&quot;renboyu010214&quot;</span>);</span><br><span class="line">            <span class="comment">//获取执行sql的对象Statement</span></span><br><span class="line">            statement=connection.createStatement();</span><br><span class="line">            <span class="comment">//执行sql语句</span></span><br><span class="line">            <span class="keyword">int</span> result=statement.executeUpdate(sql);</span><br><span class="line">            <span class="comment">//输出结果</span></span><br><span class="line">            System.out.println(result);</span><br><span class="line">        &#125; <span class="keyword">catch</span> (ClassNotFoundException | SQLException e) &#123;</span><br><span class="line">            e.printStackTrace();</span><br><span class="line">        &#125;<span class="keyword">finally</span> &#123;</span><br><span class="line">            <span class="comment">//释放资源,由于可能出错导致没有成功获取数据库连接对象和Statement，所以要提前检验是否为空</span></span><br><span class="line">            <span class="keyword">if</span>(statement!=<span class="keyword">null</span>) &#123;</span><br><span class="line">                <span class="keyword">try</span> &#123;</span><br><span class="line">                    statement.close();</span><br><span class="line">                &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                    throwables.printStackTrace();</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line">            <span class="keyword">if</span>(connection!=<span class="keyword">null</span>) &#123;</span><br><span class="line">                <span class="keyword">try</span> &#123;</span><br><span class="line">                    connection.close();</span><br><span class="line">                &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                    throwables.printStackTrace();</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="各个对象详解"><a href="#各个对象详解" class="headerlink" title="各个对象详解"></a>各个对象详解</h2><h3 id="DriverManager"><a href="#DriverManager" class="headerlink" title="DriverManager"></a>DriverManager</h3><p>驱动管理对象 </p>
<h4 id="功能"><a href="#功能" class="headerlink" title="功能"></a>功能</h4><p><strong>注册驱动</strong></p>
<p>DriverManager提供registerDriver方法注册给定的驱动程序，而我们在上面代码中所写的<code>Class.forName(&quot;com.mysql.cj.jdbc.Driver&quot;);</code>之所以能注册驱动，是因为将com.mysql.cj.jdbc.Driver加载进了内存，而com.mysql.cj.jdbc.Driver包内存在静态代码块，通过阅读源码可以找到该静态代码块</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">static</span> &#123;</span><br><span class="line">    <span class="keyword">try</span> &#123;</span><br><span class="line">        java.sql.DriverManager.registerDriver(<span class="keyword">new</span> Driver());</span><br><span class="line">    &#125; <span class="keyword">catch</span> (SQLException E) &#123;</span><br><span class="line">        <span class="keyword">throw</span> <span class="keyword">new</span> RuntimeException(<span class="string">&quot;Can&#x27;t register driver!&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>可以看到<code>Class.forName(&quot;com.mysql.cj.jdbc.Driver&quot;);</code>仍然是通过调用DriverManager提供的registerDriver方法注册驱动程序，只是这种写法比调用方法更加简洁</p>
<p>不过，自5版本后，jar包会自动帮我们注册驱动，所以其实注册驱动步骤可以省略</p>
<p><img src="https://ywrbyimg.oss-cn-chengdu.aliyuncs.com/img/%E8%87%AA%E5%8A%A8%E6%B3%A8%E5%86%8C%E9%A9%B1%E5%8A%A8.jpg" alt="自动注册驱动"></p>
<p><strong>获取数据库连接</strong></p>
<p>利用DriverManager的getConnection方法可以获取数据库连接，返回数据库连接对象</p>
<p>该方法接收三个参数，分别是</p>
<ul>
<li>url:指定连接路径，以MySQL为例：jdbc:mysql://ip地址(域名):端口号/数据库名称</li>
<li>user:用户名</li>
<li>password:密码</li>
</ul>
<h3 id="Connection"><a href="#Connection" class="headerlink" title="Connection"></a>Connection</h3><p>数据库连接对象</p>
<h4 id="功能-1"><a href="#功能-1" class="headerlink" title="功能"></a>功能</h4><p><strong>获取执行sql语句的对象</strong></p>
<ul>
<li>Statement    createStatement()</li>
<li>PreparedStatement    prepareStatement(String sql)</li>
</ul>
<p><strong>管理事务</strong></p>
<ul>
<li>开启事务：void setAutoCommit​(boolean autoCommit)  调用该方法，设置参数为false，即可开启事务<ul>
<li>在执行sql语句之前开启事务</li>
</ul>
</li>
<li>提交事务：void commit()  <ul>
<li>在所有sql语句执行完后提交事务</li>
</ul>
</li>
<li>回滚事务：void rollback()<ul>
<li>在catch中回滚事务</li>
</ul>
</li>
</ul>
<h3 id="Statement"><a href="#Statement" class="headerlink" title="Statement"></a>Statement</h3><p>执行sql语句的对象</p>
<h4 id="功能-2"><a href="#功能-2" class="headerlink" title="功能"></a>功能</h4><p><strong>执行sql语句</strong></p>
<ul>
<li>boolean    execute(String sql) 执行任意的sql语句，不常用（返回值为执行的结果）</li>
<li>int executeUpdate​(String sql) 执行DML语句和DDL语句。返回值为影响的行数，可以作为判断执行成功与否的标准</li>
<li>ResultSet    executeQuery​(String sql) 执行DQL语句</li>
</ul>
<h3 id="ResultSet"><a href="#ResultSet" class="headerlink" title="ResultSet"></a>ResultSet</h3><p>数据库结果集对象</p>
<ul>
<li>boolean next() 游标向下移动一行,返回值表示当前行是否是最后一行数据，如果是则返回false，所以可以用while循环遍历ResultSet</li>
<li>getString(),getInt,getDouble…   获取某一行中的数据，可以接收两种参数，整型参数表示数据的列数，字符串型数据表示列的名称</li>
</ul>
<h3 id="PreparedStatement"><a href="#PreparedStatement" class="headerlink" title="PreparedStatement"></a>PreparedStatement</h3><p>执行sql语句的对象</p>
<h4 id="sql注入问题"><a href="#sql注入问题" class="headerlink" title="sql注入问题"></a>sql注入问题</h4><p>在拼接sql时，有一些sql的特殊关键字参与字符串拼接，导致安全性问题。例如，下面代码</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">String userName, password;</span><br><span class="line">String sql=<span class="string">&quot;SELECT * FROM loginMess where userName =&#x27;&quot;</span>+userName+<span class="string">&quot;&#x27; and password=&#x27;&quot;</span>+password+<span class="string">&quot;&#x27;;&quot;</span>;</span><br></pre></td></tr></table></figure>
<p>假如password处用户传入<code>a&#39; or &#39;a&#39;=&#39;a&#39;</code>。则整个sql语句变为了<code>SELECT * FROM loginMess where userName =&#39;userName&#39; and password=&#39;a&#39; or &#39;a&#39;=&#39;a&#39;;</code>则整个sql语句变为恒等句，用户始终可以登录成功</p>
<h4 id="可能发生sql诸如的代码"><a href="#可能发生sql诸如的代码" class="headerlink" title="可能发生sql诸如的代码"></a>可能发生sql诸如的代码</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * 登录案例,使用PreparedStatement实现</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">LoginDemo2</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">login</span><span class="params">(String userName,String password)</span></span>&#123;</span><br><span class="line">        Connection connection=<span class="keyword">null</span>;</span><br><span class="line">        Statement statement=<span class="keyword">null</span>;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="comment">//通过工具类获取数据库连接</span></span><br><span class="line">            connection= JDBCUtils.getConnection();</span><br><span class="line">            <span class="comment">//定义sql语句</span></span><br><span class="line">            String sql=<span class="string">&quot;SELECT * FROM loginMess where userName =&#x27;&quot;</span>+userName+<span class="string">&quot;&#x27; and password=&#x27;&quot;</span>+password+<span class="string">&quot;&#x27;;&quot;</span>;</span><br><span class="line">            <span class="comment">//获取执行sql的对象Statement</span></span><br><span class="line">            statement=connection.createStatement();</span><br><span class="line">            <span class="comment">//执行sql语句</span></span><br><span class="line">            ResultSet set=statement.executeQuery(sql);</span><br><span class="line">            <span class="comment">//遍历数据库表，获得所有用户对象</span></span><br><span class="line">            <span class="keyword">if</span> (set.next())&#123;</span><br><span class="line">                System.out.println(<span class="string">&quot;登陆成功&quot;</span>);</span><br><span class="line">            &#125;<span class="keyword">else</span> &#123;</span><br><span class="line">                System.out.println(<span class="string">&quot;登陆失败&quot;</span>);</span><br><span class="line">            &#125;</span><br><span class="line">        &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">            throwables.printStackTrace();</span><br><span class="line">        &#125;<span class="keyword">finally</span> &#123;</span><br><span class="line">            <span class="comment">//通过工具类关闭资源</span></span><br><span class="line">            JDBCUtils.closeDB(connection,statement);</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">        Scanner sc=<span class="keyword">new</span> Scanner(System.in);</span><br><span class="line">        System.out.println(<span class="string">&quot;please input the username:&quot;</span>);</span><br><span class="line">        String userName=sc.nextLine();</span><br><span class="line">        System.out.println(<span class="string">&quot;please input the password:&quot;</span>);</span><br><span class="line">        String password=sc.nextLine();</span><br><span class="line">        login(userName,password);</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="解决方案"><a href="#解决方案" class="headerlink" title="解决方案"></a>解决方案</h4><p>使用PreparedStatement对象来执行sql语句，PreparedStatement对象执行预编译的sql语句，所有参数使用“?”作为占位符。借此可解决sql诸如问题</p>
<h4 id="使用PreparedStatement后的流程"><a href="#使用PreparedStatement后的流程" class="headerlink" title="使用PreparedStatement后的流程"></a>使用PreparedStatement后的流程</h4><ol>
<li>导入驱动jar包</li>
<li>注册驱动</li>
<li>获取数据库连接对象Connection</li>
<li>定义sql<ul>
<li>注意：定义的sql语句中的所有变量用通配符?代替</li>
</ul>
</li>
<li>获取执行sql语句的对象PreparedStatement（需要传入sql语句）</li>
<li>给?赋值<ul>
<li>setInt,setDouble等等方法，第一个参数为通配符?的位置，第二个参数为传入的值</li>
</ul>
</li>
<li>执行sql，接收返回结果（PreparedStatement对象的执行方法不需要传入sql语句，因为已经在定义时传入了）</li>
<li>处理结果</li>
<li>释放资源（PreparedStatement和Statement一样也需要释放）</li>
</ol>
<h4 id="使用PreparedStatement修改后的登录代码"><a href="#使用PreparedStatement修改后的登录代码" class="headerlink" title="使用PreparedStatement修改后的登录代码"></a>使用PreparedStatement修改后的登录代码</h4><p>可以避免sql诸如问题</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * 登录案例,使用PreparedStatement实现</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">LoginDemo2</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">login</span><span class="params">(String userName,String password)</span></span>&#123;</span><br><span class="line">        Connection connection=<span class="keyword">null</span>;</span><br><span class="line">        PreparedStatement preSta=<span class="keyword">null</span>;</span><br><span class="line">        ResultSet set=<span class="keyword">null</span>;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="comment">//通过工具类获取数据库连接</span></span><br><span class="line">            connection= JDBCUtils.getConnection();</span><br><span class="line">            <span class="comment">//定义sql语句，所有变量用通配符?代替</span></span><br><span class="line">            String sql=<span class="string">&quot;SELECT * FROM loginMess where userName =? and password=?;&quot;</span>;</span><br><span class="line">            <span class="comment">//获取执行sql的对象PreparedStatement</span></span><br><span class="line">            preSta=connection.prepareStatement(sql);</span><br><span class="line">            <span class="comment">//给?赋值</span></span><br><span class="line">            preSta.setString(<span class="number">1</span>,userName);</span><br><span class="line">            preSta.setString(<span class="number">2</span>,password);</span><br><span class="line">            <span class="comment">//执行sql语句(不需要传参)</span></span><br><span class="line">            set=preSta.executeQuery();</span><br><span class="line">            <span class="comment">//遍历数据库表，获得所有用户对象</span></span><br><span class="line">            <span class="keyword">if</span> (set.next())&#123;</span><br><span class="line">                System.out.println(<span class="string">&quot;登陆成功&quot;</span>);</span><br><span class="line">            &#125;<span class="keyword">else</span> &#123;</span><br><span class="line">                System.out.println(<span class="string">&quot;登陆失败&quot;</span>);</span><br><span class="line">            &#125;</span><br><span class="line">        &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">            throwables.printStackTrace();</span><br><span class="line">        &#125;<span class="keyword">finally</span> &#123;</span><br><span class="line">            <span class="comment">//通过工具类关闭资源</span></span><br><span class="line">            JDBCUtils.closeDB(set,connection,preSta);</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">        Scanner sc=<span class="keyword">new</span> Scanner(System.in);</span><br><span class="line">        System.out.println(<span class="string">&quot;please input the username:&quot;</span>);</span><br><span class="line">        String userName=sc.nextLine();</span><br><span class="line">        System.out.println(<span class="string">&quot;please input the password:&quot;</span>);</span><br><span class="line">        String password=sc.nextLine();</span><br><span class="line">        login(userName,password);</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>


<h2 id="定义JDBC工具类简化代码"><a href="#定义JDBC工具类简化代码" class="headerlink" title="定义JDBC工具类简化代码"></a>定义JDBC工具类简化代码</h2><h3 id="工具类"><a href="#工具类" class="headerlink" title="工具类"></a>工具类</h3><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * JDBC工具类</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">JDBCUtils</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//定义各个静态遍历</span></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> String url;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> String user;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> String password;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> String driver;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 静态代码块，只在创建时调用一次</span></span><br><span class="line"><span class="comment">     * 可以在此处进行配置文件的读取，以及驱动注册等步骤</span></span><br><span class="line"><span class="comment">     *</span></span><br><span class="line"><span class="comment">     * 将url，user，password，driver等变量</span></span><br><span class="line"><span class="comment">     * 存入配置文件并读取可以提高代码复用性</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="keyword">static</span> &#123;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="comment">//创建配置文件数据集</span></span><br><span class="line">            Properties pro=<span class="keyword">new</span> Properties();</span><br><span class="line">            <span class="comment">//创建类加载器classLoader</span></span><br><span class="line">            ClassLoader classLoader=JDBCUtils.class.getClassLoader();</span><br><span class="line">            <span class="comment">//通过类加载器获取在src下的配置文件，这样可以避免绝对路径带来的问题</span></span><br><span class="line">            URL res=classLoader.getResource(<span class="string">&quot;jdbc.properties&quot;</span>);</span><br><span class="line">            String path=res.getPath();</span><br><span class="line">            <span class="comment">//加载配置文件</span></span><br><span class="line">            pro.load(<span class="keyword">new</span> FileReader(path));</span><br><span class="line"></span><br><span class="line">            <span class="comment">//获取配置文件中的数据</span></span><br><span class="line">            url=pro.getProperty(<span class="string">&quot;url&quot;</span>);</span><br><span class="line">            user=pro.getProperty(<span class="string">&quot;user&quot;</span>);</span><br><span class="line">            password=pro.getProperty(<span class="string">&quot;password&quot;</span>);</span><br><span class="line">            driver=pro.getProperty(<span class="string">&quot;driver&quot;</span>);</span><br><span class="line"></span><br><span class="line">            <span class="comment">//注册驱动</span></span><br><span class="line">            Class.forName(driver);</span><br><span class="line">        &#125; <span class="keyword">catch</span> (IOException | ClassNotFoundException e) &#123;</span><br><span class="line">            e.printStackTrace();</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 获取数据库连接</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@return</span> 数据库连接</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@throws</span> SQLException</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Connection <span class="title">getConnection</span><span class="params">()</span> <span class="keyword">throws</span> SQLException </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> DriverManager.getConnection(url,user,password);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 关闭数据库相关资源</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> rs ResultSet数据库结果集对象</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> connection 数据库连接对象</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> statement sql语句执行对象</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">closeDB</span><span class="params">(ResultSet rs,Connection connection,Statement statement)</span></span>&#123;</span><br><span class="line">        <span class="keyword">if</span>(rs!=<span class="keyword">null</span>)&#123;</span><br><span class="line">            <span class="keyword">try</span> &#123;</span><br><span class="line">                rs.close();</span><br><span class="line">            &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                throwables.printStackTrace();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span>(statement!=<span class="keyword">null</span>)&#123;</span><br><span class="line">            <span class="keyword">try</span> &#123;</span><br><span class="line">                statement.close();</span><br><span class="line">            &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                throwables.printStackTrace();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span>(connection!=<span class="keyword">null</span>)&#123;</span><br><span class="line">            <span class="keyword">try</span> &#123;</span><br><span class="line">                connection.close();</span><br><span class="line">            &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                throwables.printStackTrace();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 关闭数据库相关资源</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> connection 数据库连接对象</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> statement sql语句执行对象</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">closeDB</span><span class="params">(Connection connection,Statement statement)</span></span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span>(statement!=<span class="keyword">null</span>)&#123;</span><br><span class="line">            <span class="keyword">try</span> &#123;</span><br><span class="line">                statement.close();</span><br><span class="line">            &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                throwables.printStackTrace();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span>(connection!=<span class="keyword">null</span>)&#123;</span><br><span class="line">            <span class="keyword">try</span> &#123;</span><br><span class="line">                connection.close();</span><br><span class="line">            &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">                throwables.printStackTrace();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="配置文件"><a href="#配置文件" class="headerlink" title="配置文件"></a>配置文件</h3><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">url=jdbc:mysql:<span class="comment">//cdb-cd3ybvc6.cd.tencentcdb.com:10056/weixinNews</span></span><br><span class="line">user=root</span><br><span class="line">password=rby</span><br><span class="line">driver=com.mysql.cj.jdbc.Driver</span><br></pre></td></tr></table></figure>

<h3 id="测试类"><a href="#测试类" class="headerlink" title="测试类"></a>测试类</h3><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">JDBCDemo3</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line">        Connection connection=<span class="keyword">null</span>;</span><br><span class="line">        Statement statement=<span class="keyword">null</span>;</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="comment">//通过工具类获取数据库连接</span></span><br><span class="line">            connection= JDBCUtils.getConnection();</span><br><span class="line">            <span class="comment">//定义sql语句</span></span><br><span class="line">            String sql=<span class="string">&quot;SELECT * FROM WEIBO WHERE TITLE LIKE &#x27;%韩国%&#x27;;&quot;</span>;</span><br><span class="line">            <span class="comment">//获取执行sql的对象Statement</span></span><br><span class="line">            statement=connection.createStatement();</span><br><span class="line">            <span class="comment">//执行sql语句</span></span><br><span class="line">            ResultSet set=statement.executeQuery(sql);</span><br><span class="line">            <span class="comment">//打印结果</span></span><br><span class="line">            <span class="keyword">while</span> (set.next())&#123;</span><br><span class="line">                String title=set.getString(<span class="string">&quot;TITLE&quot;</span>);</span><br><span class="line">                System.out.println(title);</span><br><span class="line">            &#125;</span><br><span class="line">        &#125; <span class="keyword">catch</span> (SQLException throwables) &#123;</span><br><span class="line">            throwables.printStackTrace();</span><br><span class="line">        &#125;<span class="keyword">finally</span> &#123;</span><br><span class="line">            <span class="comment">//通过工具类关闭资源</span></span><br><span class="line">            JDBCUtils.closeDB(connection,statement);</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">Author: </span><span class="post-copyright-info"><a href="mailto:undefined">Ywrby</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">Link: </span><span class="post-copyright-info"><a href="http://ywrby.cn/2021/03/03/4-JDBC/">http://ywrby.cn/2021/03/03/4-JDBC/</a></span></div><div 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class="social-icon" href="http://wpa.qq.com/msgrd?v=3&amp;uin=2278431384&amp;site=qq&amp;menu=yes" target="_blank" title="QQ"><i class="fab fa-qq"></i></a><a class="social-icon" href="https://twitter.com/ywrby1" target="_blank" title="Twitter"><i class="fab fa-twitter"></i></a><a class="social-icon" href="https://www.facebook.com/profile.php?id=100033741068822" target="_blank" title="Facebook"><i class="fab fa-facebook"></i></a></div></div><div class="card-widget card-announcement"><div class="item-headline"><i class="fas fa-bullhorn card-announcement-animation"></i><span>Announcement</span></div><div class="announcement_content">Less is more</div></div><div class="sticky_layout"><div class="card-widget" id="card-toc"><div class="item-headline"><i class="fas fa-stream"></i><span>Catalog</span></div><div class="toc-content"><ol class="toc"><li class="toc-item toc-level-1"><a class="toc-link" href="#JDBC-Java%E6%95%B0%E6%8D%AE%E5%BA%93%E8%BF%9E%E6%8E%A5"><span class="toc-number">1.</span> <span class="toc-text">JDBC Java数据库连接</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#Java-Database-Connectivity"><span class="toc-number">1.0.1.</span> <span class="toc-text">(Java Database Connectivity)</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#JDBC%E6%9C%AC%E8%B4%A8"><span class="toc-number">1.1.</span> <span class="toc-text">JDBC本质</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%9F%BA%E6%9C%AC%E6%B5%81%E7%A8%8B"><span class="toc-number">1.2.</span> <span class="toc-text">基本流程</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#%E6%9B%B4%E8%A7%84%E8%8C%83%E7%9A%84%E6%B5%81%E7%A8%8B"><span class="toc-number">1.2.0.1.</span> <span class="toc-text">更规范的流程</span></a></li></ol></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%90%84%E4%B8%AA%E5%AF%B9%E8%B1%A1%E8%AF%A6%E8%A7%A3"><span class="toc-number">1.3.</span> <span class="toc-text">各个对象详解</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#DriverManager"><span class="toc-number">1.3.1.</span> <span class="toc-text">DriverManager</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#%E5%8A%9F%E8%83%BD"><span class="toc-number">1.3.1.1.</span> <span class="toc-text">功能</span></a></li></ol></li><li class="toc-item toc-level-3"><a class="toc-link" href="#Connection"><span class="toc-number">1.3.2.</span> <span class="toc-text">Connection</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#%E5%8A%9F%E8%83%BD-1"><span class="toc-number">1.3.2.1.</span> <span class="toc-text">功能</span></a></li></ol></li><li class="toc-item toc-level-3"><a class="toc-link" href="#Statement"><span class="toc-number">1.3.3.</span> <span class="toc-text">Statement</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#%E5%8A%9F%E8%83%BD-2"><span class="toc-number">1.3.3.1.</span> <span class="toc-text">功能</span></a></li></ol></li><li class="toc-item toc-level-3"><a class="toc-link" href="#ResultSet"><span class="toc-number">1.3.4.</span> <span class="toc-text">ResultSet</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#PreparedStatement"><span class="toc-number">1.3.5.</span> <span class="toc-text">PreparedStatement</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#sql%E6%B3%A8%E5%85%A5%E9%97%AE%E9%A2%98"><span class="toc-number">1.3.5.1.</span> <span class="toc-text">sql注入问题</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#%E5%8F%AF%E8%83%BD%E5%8F%91%E7%94%9Fsql%E8%AF%B8%E5%A6%82%E7%9A%84%E4%BB%A3%E7%A0%81"><span class="toc-number">1.3.5.2.</span> <span class="toc-text">可能发生sql诸如的代码</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#%E8%A7%A3%E5%86%B3%E6%96%B9%E6%A1%88"><span class="toc-number">1.3.5.3.</span> <span class="toc-text">解决方案</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#%E4%BD%BF%E7%94%A8PreparedStatement%E5%90%8E%E7%9A%84%E6%B5%81%E7%A8%8B"><span class="toc-number">1.3.5.4.</span> <span class="toc-text">使用PreparedStatement后的流程</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#%E4%BD%BF%E7%94%A8PreparedStatement%E4%BF%AE%E6%94%B9%E5%90%8E%E7%9A%84%E7%99%BB%E5%BD%95%E4%BB%A3%E7%A0%81"><span class="toc-number">1.3.5.5.</span> <span class="toc-text">使用PreparedStatement修改后的登录代码</span></a></li></ol></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%AE%9A%E4%B9%89JDBC%E5%B7%A5%E5%85%B7%E7%B1%BB%E7%AE%80%E5%8C%96%E4%BB%A3%E7%A0%81"><span class="toc-number">1.4.</span> <span class="toc-text">定义JDBC工具类简化代码</span></a><ol 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